A storage battery system is known which is equipped with an equalizing apparatus which uniformly adjusts a variation of terminal voltage between storage batteries in an assembled battery made up of a plurality of series connected storage batteries. In the conventional method, the terminal voltages of the storage batteries are detected, and each of the storage batteries is discharged if the voltage difference between the terminal voltage of the storage battery and the minimum terminal voltage is equal to or greater than a threshold value; thus, the variation of terminal voltage between the storage batteries is controlled (see PTL 1 below).